Lignin extraction-sulfonic acid modification integrated preparation method based on eutecticevaporate solvent coupled microwave, lignin sulfonate and application

Abstract

The invention provides a lignin extraction-sulfonic acid modification integrated preparation method based on eutecticevaporate solvent coupling microwaves, lignin sulfonate and application, and belongs to the technical field of oilfield chemistry. The preparation method comprises the following steps: mixing choline chloride, epichlorohydrin and 4-hydroxybenzenesulfonic acid, heating and stirring to obtain a deep eutectic solvent ternary system; the method comprises the following steps: adding biomass powder into a deep eutectic solvent ternary system, and reacting under a microwave condition; after the reaction is completed, filtering, and adjusting the pH value of the obtained filtrate to be neutral to obtain a mixed solution; and then adding an organic solvent into the obtained mixed solution for precipitation, filtering, washing and drying to complete lignin extraction-sulfonic acid modification. According to the method, in-situ grafting of sulfonic acid functional groups is realized in the lignin separation process through the ternary eutectic solvent in combination with microwave-assisted extraction, so that sulfonation modification of lignin is completed. After sulfonation modification, the obtained sulfonated lignin is applied to the drilling fluid, and the viscosity reduction effect can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for integrated preparation of lignin extraction-sulfonic acid modification based on eutectic solvent coupling microwave, sulfonated lignin and application, belonging to the technical field of oil field chemistry. BACKGROUND

[0002] Fossil resources are consumed as bulk chemical raw materials and industrial fuels in large quantities. Due to limited reserves and non-renewable, the development and utilization of alternative resources has been a hot research field. Wood fiber, as an important biomass material, has a huge reserve and is renewable, and is considered as an effective carbon-containing resource, which can be used to alleviate the shortage of fossil resources. Among them, lignin is derived from wood fiber and is the only renewable high molecular aromatic polymer in nature. At present, lignin, a byproduct of the pulp and paper industry, is the main source of industrial lignin. However, most of the industrial lignin is used as fuel for heat recovery, and the utilization rate of high value is low, which not only increases the environmental burden, but also to some extent is not conducive to the sustainable development of resources.

[0003] Among them, sulfonated lignin as an important application field of industrial lignin is widely used in dye dispersant, pesticide dispersant, concrete water reducing agent, drilling fluid viscosity reducer and coal water slurry dispersant, and the earliest sulfonated lignin comes from the by-product of sulfite pulping process. According to the different pH values of the cooking liquor, it is divided into acid (pH value = 2-5), neutral (pH value = 5-7), and alkaline (pH value = 9-13.5) to cause lignin to be removed / dissolved in the cooking liquor. The phenolic structure units in lignin can be converted into unstable quinone intermediates, and then sulfonic acid groups are formed. However, the pH conditions of sulfite pulping are widely used, so the structure of sulfonated lignin produced has great difference. On the other hand, lignin sulfonate has high water solubility, and after cooking and pulping, sulfonated lignin will remain in the pulping waste liquid, and the waste liquid also contains hemicellulose and residual chemicals, which leads to low purity of lignin sulfonate produced by sulfite process, accounting for 50%~80% of the total mass of solids, 30% of hemicellulose, and about 10% of inorganic matter. There is also a sulfite lignin which is sulfonated by hydroxylated reaction of formaldehyde and Na2SO3 as sulfonating reagent. The hydroxypropyl sulfonation method is an environmentally friendly and efficient lignin sulfonation method, which avoids the use of formaldehyde. These traditional sulfonated lignin methods mainly use inorganic salt (Na2SO3, NaHSO3, H2SO4, etc.) sulfonating reagent to sulfonate the active sites in the side chain of lignin, and the process is relatively mature and has been widely used in the production of commercial lignin sulfonate. For example, Chinese patent document CN105601943A provides a method for preparing sulfonated lignin from sulfite papermaking waste liquid, which comprises the following steps: first, the sulfite papermaking waste liquid is treated by membrane to obtain a membrane concentrate, then the membrane concentrate is sequentially subjected to sulfonation and condensation to obtain sulfonated lignin. The membrane concentrate is subjected to sulfur dioxide sulfonation reaction, sodium bisulfite sulfonation reaction, or sodium sulfite sulfonation reaction. However, such lignin sulfonation process is faced with problems such as low purity, product structure diversification, insufficient content of sulfonic acid groups, high energy consumption, and complicated steps, which makes it difficult to apply in high-end fields.

[0004] In summary, there are great challenges in how to realize high-purity extraction of sulfonated lignin, increase the content of sulfonic acid groups, and simplify the separation and purification steps after reaction. Therefore, it is urgent to develop an efficient sulfonated lignin method to realize large-scale application of sulfonated lignin. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a lignin extraction-sulfonic acid modification integrated preparation method based on low eutectic solvent coupling microwave, sulfonated lignin and application. The present application constructs a ternary low eutectic solvent (DES) through the interaction of choline chloride (ChCl), epichlorohydrin (ECH) and 4-hydroxybenzenesulfonic acid (4-HBSA), and combines with microwave-assisted extraction to realize in-situ grafting of sulfonic acid functional groups during lignin separation, thereby completing the sulfonation modification of lignin. After sulfonation modification, the solubility of lignin in water is significantly improved, and the hydrogen bonds and polar forces between clay particles are weakened through adsorption, thereby destroying the spatial network structure of clay particles. In addition, the electronegativity of the sulfonic acid group enhances the negative charge on the surface of the clay particles, further improves the electrostatic repulsion between the particles, and prevents the aggregation of the clay particles. When the clay particles are applied as a viscosity reducer in drilling fluid, excellent viscosity reduction effect can be achieved.

[0006] The technical scheme of the present application is as follows: A lignin extraction-sulfonic acid modification integrated preparation method based on low eutectic solvent coupling microwave, comprising the following steps: (1) Mix choline chloride (ChCl), epichlorohydrin (ECH) and 4-hydroxybenzenesulfonic acid (4-HBSA), heat and stir until a uniform transparent liquid is formed to obtain a low eutectic solvent (DES) ternary system; (2) Add biomass powder to the low eutectic solvent (DES) ternary system obtained in step (1) and react under microwave conditions; after the reaction is completed, filter, adjust the pH of the obtained filtrate to neutral, and obtain a mixed solution; then add ethanol to the obtained mixed solution for precipitation, and after filtration, washing and drying, lignin extraction-sulfonic acid modification is completed to obtain sulfonated lignin for environmentally friendly water-based drilling fluid.

[0007] According to the present application, the molar ratio of choline chloride (ChCl), epichlorohydrin (ECH) and 4-hydroxybenzenesulfonic acid (4-HBSA) in step (1) is 1: (1-4): (5-20), and further preferably 1:2:10.

[0008] According to the present application, the temperature of the heating and stirring in step (1) is 40-70°C, and further preferably 60°C.

[0009] According to the present application, the biomass powder in step (2) is wheat straw powder, corn straw powder or birch stem powder, and further preferably birch stem powder; the particle size of the biomass powder is 500-1000 nm.

[0010] According to the present application, the mass ratio of the biomass powder to the low eutectic solvent (DES) ternary system in step (2) is 1:8-15, and further preferably 1:10.

[0011] According to the application, preferably, the power of the microwave in step (2) is 800-1300W, and more preferably 1000W.

[0012] According to the application, preferably, the temperature of the reaction in step (2) is 60-100℃, and more preferably 80℃; and the time of the reaction is 1-8h, and more preferably 4-5h.

[0013] According to the application, preferably, in step (2), the pH is adjusted to neutral by using a hydrochloric acid aqueous solution with a concentration of 1wt%.

[0014] According to the application, preferably, the volume ratio of the ethanol to the mixed solution in step (2) is 1-4:1; and the time of the precipitation is 20-40min.

[0015] According to the application, preferably, the washing in step (2) is washing by using anhydrous ethanol; and the drying is vacuum drying at 60-70℃ for 15-20h.

[0016] An environment-friendly sulfonated lignin for water-based drilling fluid is obtained by the above preparation method.

[0017] According to the application, the environment-friendly sulfonated lignin for water-based drilling fluid is applied as a viscosity reducer in the environment-friendly water-based drilling fluid, and the addition amount of the environment-friendly sulfonated lignin for water-based drilling fluid in the environment-friendly water-based drilling fluid is 3-6wt%.

[0018] The technical features and beneficial effects of the application are as follows: 1. The application uses a low eutectic solvent with a specific composition, choline chloride (ChCL) as a hydrogen bond acceptor, epichlorohydrin (ECH) as a hydrogen bond acceptor and crosslinking agent, and 4-hydroxybenzenesulfonic acid (4-HBSA) as a hydrogen bond donor and sulfonating agent, and combines with microwave enhanced reaction to realize the integration of lignin extraction and sulfonic acid modification. Specifically, under the action of microwave irradiation, the ternary system of the low eutectic solvent (DES) selectively breaks the lignin-carbohydrate complex in biomass, directionally dissociates lignin, and destroys the intramolecular and intermolecular hydrogen bonds (such as phenolic hydroxyl and ether bond) of lignin, so that the lignin structure is loose and more active sites (such as phenolic hydroxyl and aliphatic hydroxyl) are exposed. Based on the ring-opening reaction mechanism, epichlorohydrin in DES can react with phenolic hydroxyl in lignin and hydroxyl in 4-hydroxybenzenesulfonic acid at the same time, and the sulfonic acid functional group is grafted to the surface of lignin, so as to realize the sulfonation modification of lignin. The method solves the problems of high pollution, high energy consumption, and complicated steps in the traditional lignin sulfonation process.

[0019] 2. This invention improves the utilization rate of lignin, reduces the use of lignin as a by-product of the pulp and paper industry, reduces the environmental burden to a certain extent, and is conducive to the sustainable development of resources.

[0020] 3. The selectivity of the eutectic solvent allows it to preferentially dissolve lignin while neglecting other components (such as cellulose and hemicellulose), thus achieving efficient lignin extraction. 4-Hydroxybenzenesulfonic acid (4-HBSA) acts as both a hydrogen bond donor and a sulfonating agent in the DES system, completing the sulfonation modification of lignin during extraction and providing sulfonic acid groups (-SO3H) to directly participate in the sulfonation reaction. Furthermore, epichlorohydrin (ECH) acts as both a hydrogen bond acceptor and a cross-linking agent. On one hand, it enhances the stability and solubility of the system by forming a hydrogen bond network with other components in the DES; on the other hand, it effectively grafts sulfonic acid functional groups onto the lignin surface through a ring-opening reaction with the active hydroxyl groups in lignin molecules and the hydroxyl groups in 4-HBSA molecules.

[0021] 4. The lignin sulfonate obtained by this invention possesses multiple active groups such as aromatic groups, phenolic hydroxyl groups, alcoholic hydroxyl groups, carbonyl groups, carboxyl groups, and sulfonic acid groups. It also has advantages such as being renewable, biodegradable, and non-toxic. In drilling fluids, it is mainly used as a viscosity reducer and filtration reducer. Furthermore, the carboxyl and sulfonic acid groups are anionic groups with strong hydration characteristics and good water solubility. They can form a strong solvation layer on the polymer chain, thereby providing resistance to salt, temperature, and pollution, further expanding the application range of the viscosity reducer.

[0022] 5. The sulfonated lignin obtained by this invention, when used as a viscosity reducer in water-based drilling fluids, has the advantages of significant viscosity reduction, high temperature resistance, and salt and shear resistance. The prepared sulfonated lignin has a viscosity reduction rate of more than 86% in fresh water-based slurry at a temperature of 200-240℃; the shear stable viscosity is not higher than 37 mPa·s; and the salt resistance rate is greater than 38%, which can meet the high temperature environment of deep wells and is convenient for field application. Attached Figure Description

[0023] Figure 1 The infrared spectrum of sulfonated lignin for the environmentally friendly water-based drilling fluid prepared in Example 1. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0025] All raw materials used in the embodiments are conventional and commercially available; unless otherwise specified, the methods described are existing technologies. All other examples based on the embodiments of this invention, modified or refined by those skilled in the art, fall within the scope of protection of this invention.

[0026] Example 1 An integrated preparation method for lignin extraction and sulfonic acid modification based on microwave coupling with a eutectic solvent includes the following steps: (1) Choline chloride (ChCl), epichlorohydrin (ECH), and 4-hydroxybenzenesulfonic acid (4-HBSA) were mixed in a molar ratio of 1:2:10 and heated and stirred at 60°C until a homogeneous transparent liquid was formed, thus obtaining a ternary system of eutectic solvent (DES).

[0027] (2) Birch trunk powder (particle size of 800 nm) was added to the ternary system of eutectic solvent (DES) obtained in step (1). The mass ratio of birch trunk powder to eutectic solvent (DES) ternary system was 1:10. The reaction was carried out at 80℃ and 1000W microwave assisted conditions for 4.5 h. After the reaction was completed, the mixture was filtered and the pH of the filtrate was adjusted to neutral with a 1wt% hydrochloric acid aqueous solution to obtain a mixture. Ethanol was added to the mixture for precipitation for 30 min. The volume ratio of ethanol to the mixture was 2:1. After filtration, the precipitate was washed with ethanol 3 times to remove residual impurities and unreacted reactants. The precipitate was vacuum dried at 65℃ for 18 h to complete the lignin extraction-sulfonic acid modification and obtain environmentally friendly water-based drilling fluid sulfonated lignin.

[0028] The infrared spectrum of the sulfonated lignin used in the environmentally friendly water-based drilling fluid obtained in this embodiment is as follows: Figure 1 As shown, by Figure 1 It can be known that 3408cm -1 The characteristic peak is caused by the vibrations of phenolic and alcoholic hydroxyl groups in lignin and the intermolecular hydrogen bonds they form, at 2931 cm⁻¹. -1 The vibrations at 1510 cm⁻¹ are caused by the vibrations of the methyl (-CH₃) and methylene (-CH₂-) groups on the lignin side chains. -1 The location is due to the vibration of the benzene ring skeleton (C=C) in lignin, 1419cm -1 The position is due to in-plane bending coupling of CH and the vibration of the aromatic ring skeleton. 1132cm -1 It originates from the vibration of aromatic ether COC in lignin, 1037 cm⁻¹ -1 The characteristic peak at this point is the most fundamental difference between lignin and sulfonated lignin. This peak is caused by the vibration of the -SO3 sulfonic acid group, which originates from the symmetric stretching vibration of the S=O group in the sulfonic acid group. This indicates that the lignin has undergone a sulfonation reaction, successfully introducing a hydrophilic sulfonic acid group onto the lignin. (866 cm⁻¹)-1 is caused by the C-H out-of-plane bending vibration of lignin.

[0029] Example 2 A lignin extraction-sulfonic acid modification integrated preparation method based on deep eutectic solvent coupling microwave was as described in Example 1, except that the molar ratio of choline chloride (ChCl), epichlorohydrin (ECH), and 4-hydroxybenzenesulfonic acid (4-HBSA) in step (1) was 1:2:5.

[0030] Example 3 A lignin extraction-sulfonic acid modification integrated preparation method based on deep eutectic solvent coupling microwave was as described in Example 1, except that the molar ratio of choline chloride (ChCl), epichlorohydrin (ECH), and 4-hydroxybenzenesulfonic acid (4-HBSA) in step (1) was 1:2:15.

[0031] Example 4 A lignin extraction-sulfonic acid modification integrated preparation method based on deep eutectic solvent coupling microwave was as described in Example 1, except that the molar ratio of choline chloride (ChCl), epichlorohydrin (ECH), and 4-hydroxybenzenesulfonic acid (4-HBSA) in step (1) was 1:1:10.

[0032] Example 5 A lignin extraction-sulfonic acid modification integrated preparation method based on deep eutectic solvent coupling microwave was as described in Example 1, except that the molar ratio of choline chloride (ChCl), epichlorohydrin (ECH), and 4-hydroxybenzenesulfonic acid (4-HBSA) in step (1) was 1:3:10.

[0033] Example 6 A lignin extraction-sulfonic acid modification integrated preparation method based on deep eutectic solvent coupling microwave was as described in Example 1, except that the mass ratio of birch stem powder to deep eutectic solvent (DES) ternary system in step (2) was 1:5.

[0034] Example 7 A lignin extraction-sulfonic acid modification integrated preparation method based on deep eutectic solvent coupling microwave was as described in Example 1, except that the mass ratio of birch stem powder to deep eutectic solvent (DES) ternary system in step (2) was 1:15.

[0035] Example 8 A lignin extraction-sulfonic acid modification integrated preparation method based on deep eutectic solvent coupling microwave was as described in Example 1, except that the power of the microwave in step (2) was 800W.

[0036] Example 9 A method for preparing modified lignin by lignin extraction and sulfonic acid modification based on deep eutectic solvent coupled with microwave is as described in Embodiment 1, except that the power of the microwave in step (2) is 1200 W.

[0037] Embodiment 10 A method for preparing modified lignin by lignin extraction and sulfonic acid modification based on deep eutectic solvent coupled with microwave is as described in Embodiment 1, except that the birch stem powder in step (2) is replaced by corn straw powder (particle size of 800 nm).

[0038] Comparative Example 1 A method for preparing modified lignin for an environmentally friendly water-based drilling fluid is as described in Embodiment 1, except that 4-hydroxybenzenesulfonic acid (4-HBSA) is not added in step (1).

[0039] Comparative Example 2 A method for preparing modified lignin for an environmentally friendly water-based drilling fluid is as described in Embodiment 1, except that epichlorohydrin (ECH) is not added in step (1).

[0040] Comparative Example 3 A method for preparing modified lignin for an environmentally friendly water-based drilling fluid is as described in Embodiment 1, except that the reaction in step (2) is performed at 80°C in a water bath for 4.5 h.

[0041] Comparative Example 4 Sulfonated lignin is prepared using a traditional sulfite pulping process, using sodium sulfite as a sulfonation agent, and a reaction temperature of 180°C to obtain sulfonated lignin, and the specific steps are as follows: (1) First, 5 g of birch stem powder is mixed with 200 mL of deionized water, 0.5 mg of sodium sulfite and 8 g of sodium hydroxide are added to form a reaction slurry; (2) The reaction slurry is heated to 180°C and maintained in a 1 MPa pressure vessel for 6 h. During this process, sodium sulfite and lignin in the wood undergo a chemical reaction, converting lignin into lignin sulfonate; (3) The obtained solution is filtered to obtain a filtrate, and sodium hydroxide is added to adjust the pH of the filtrate to 10. The lignin sulfonate is separated by centrifugation, and the obtained precipitate is freeze-dried (-65°C, 24 h) to obtain sulfonated lignin.

[0042] Comparative Example 5 A method for preparing modified lignin for an environmentally friendly water-based drilling fluid is as described in Embodiment 1, except that epichlorohydrin is replaced by urea in step (1).

[0043] Comparative Example 6 A method for preparing a modified lignin for use in an environmentally friendly water-based drilling fluid is as described in Example 1, except that in step (1) the epichlorohydrin is replaced with lactic acid.

[0044] Comparative Example 7 A method for preparing a modified lignin for use in an environmentally friendly water-based drilling fluid is as described in Example 1, except that in step (1) the 4-hydroxybenzenesulfonic acid is replaced with sulfamic acid.

[0045] Comparative Example 8 A method for preparing a modified lignin for use in an environmentally friendly water-based drilling fluid is as described in Example 1, except that in step (1) the 4-hydroxybenzenesulfonic acid is replaced with sodium sulfite.

[0046] Test Example 1 The sulfonate group content of the sulfonated lignins prepared in the Examples and Comparative Examples is tested using a two-phase titration method to determine the content of the sulfonate group characteristic functional group of the resulting sulfonated lignin, according to the following procedure: Preparation of solvents for the experiment: 1.75 g of Himin 1622 is accurately weighed, dissolved in water, and made up to a 250 mL volumetric flask to obtain a stock solution; immediately before use, 25.00 mL of the stock solution is accurately transferred, diluted with ultrapure water, and made up to a 250 mL volumetric flask to obtain a standard solution; 5.44 g of sodium sulfate and 2.52 g of anhydrous sodium sulfate are weighed and dissolved in 400 mL of ultrapure water, followed by the addition of 5.0 mL of concentrated sulfuric acid, stirring to homogeneity, cooling, and making up to 500 mL with ultrapure water to obtain the acidic buffer solution (pH about 3) used for testing; 0.5 g of blue disulfide VN150 and 0.25 g of acid blue-1 are dissolved in ultrapure water and made up to a 250 mL volumetric flask to obtain the indicator solution.

[0047] Sample pretreatment: 0.1 g of the dried sulfonated lignin sample (accurate to 0.0001 g) is accurately weighed into a beaker, dissolved with a small amount of ultrapure water, and lightly heated or ultrasonically assisted to dissolve. The solution is quantitatively transferred to a separatory funnel, washed with a small amount of chloroform 2-3 times to remove non-polar organic impurities that may be present in the sample, the organic phase is discarded, and the aqueous phase is retained to obtain the sample solution.

[0048] Specific test method: accurately take a certain amount of sample solution (or pre-processed aqueous phase) in a dry 250 mL iodometric flask with a stopper, add 10 mL of acid buffer, 10 mL of chloroform, and 0.5-1.0 mL of indicator solution in turn. Titrate with the hemin 1622 standard solution, start with a faster speed, and shake the iodometric flask vigorously (pay attention to air release) to make the two phases fully contact. When approaching the end point, add drop by drop or even half drop, and shake well. When the organic phase (lower chloroform phase) changes from pink or colorless to persistent blue-gray or blue, and the aqueous phase color becomes lighter or almost colorless, record the volume V (mL) of hemin 1622 standard solution consumed. Blank experiment: the rest of the steps are exactly the same except that no sample is added. Perform blank titration and record the volume V0 (mL) of hemin 1622 standard solution consumed. Calculate the total content of sulfonate groups according to the following formula, and the test results are shown in Table 1.

[0049] (1) In formula (1): V: volume of hemin 1622 standard solution consumed by the sample, mL; V0: volume of hemin 1622 standard solution consumed by the blank, mL; C: concentration of hemin 1622 standard solution, mol / L; m: mass of the sample taken, g; 1000: unit conversion coefficient. The test results are shown in Table 1.

[0050] Table 1 Sulfonate group content

[0051] The test results show that the sulfonate group content of the lignin sulfonate in Example 1 is 1.22 mmol / g. Example 2 reduces the amount of 4-hydroxybenzenesulfonic acid (4-HBSA) in the eutectic solvent ternary system. When the content of 4-HBSA is less, the sulfonating agent of the system may be insufficient, the number of sulfonate groups (-SO3H) introduced into the lignin molecule is limited, the reaction kinetics is limited, the activation energy is difficult to overcome, the sulfonation rate is slow, the overall reaction time is prolonged, and the sulfonate group content of the final product is reduced. Example 3 increases the amount of 4-hydroxybenzenesulfonic acid (4-HBSA) in the eutectic solvent ternary system. When the content of 4-HBSA is more, the system may be too acidic, which may cause self-degradation of lignin, further reducing the number of active sites on the lignin molecule. At the same time, it may also greatly increase the viscosity of the system, affecting the efficiency of lignin sulfonation modification, and reducing the content of sulfonate groups. Moreover, too much sulfonating agent may cause side reactions, such as cross-linking between sulfonic acid groups, the generation of by-products (such as low molecular weight sulfates), resulting in reduced purity of the modified lignin sulfonate, complex post-treatment, and affecting performance consistency and subsequent use. Example 4 reduces the amount of epichlorohydrin (ECH) in the eutectic solvent ternary system. When the content of ECH is less, the cross-linking degree of the system is insufficient, and the degree of sulfonation is low, so the content of sulfonate groups is reduced. Example 5 increases the amount of epichlorohydrin (ECH) in the eutectic solvent ternary system. When the content of ECH is more, the viscosity of the system is too high, and the high cross-linking degree of the DES system makes it difficult for the aromatic ring of lignin to be attacked by the sulfonating agent. In addition, the high cross-linking solvent may compete or interfere with the hydrogen bonds between lignin molecules, thereby affecting the extraction and modification efficiency of lignin, and thus reducing the content of sulfonate groups. In Example 6, the amount of DES is reduced, resulting in insufficient functional groups of DES, which cannot fully break the hydrogen bond network in biomass, and cannot effectively extract lignin, so the content of sulfonate groups in the final product is reduced. In Example 7, the amount of DES is increased, although it increases the contact area between DES and biomass, but the high concentration of DES changes the polarity of the reaction system, resulting in poor swelling of lignin, and -SO3H is difficult to contact with phenolic hydroxyl active sites, so the reaction efficiency is slightly reduced. At the same time, it increases the cost of lignin sulfonate extraction, and further increases the cost in the subsequent separation and purification process, which is not economically beneficial. Microwave heating can reduce the viscosity of DES and improve mass transfer, but a suitable microwave intensity is needed. When the microwave intensity in Example 8 is 800W, the local temperature does not reach the temperature of the lignin sulfonation reaction, so the content of sulfonate groups is reduced. The microwave intensity in Example 9 is higher, which may cause the sulfonate groups and ether bonds in the lignin sulfonate to break, and may also cause more side reactions (condensation or degradation of lignin) to occur, resulting in desulfonation or polymerization of the lignin sulfonate, affecting the molecular weight and activity of the product.Based on the analysis of the examples and comparative examples, example 1 is the best experimental condition of the lignin extraction-sulfonated modification integrated preparation method based on the eutectic solvent coupling microwave.

[0052] Test example 2 The sulfonated lignin prepared in the examples and comparative examples was tested in the drilling fluid, and the test results are shown in Table 2, and the test method is as follows: (1) Preparation of fresh water base slurry: 400 mL of deionized water was added to a high-speed stirring cup, and high-speed stirring was started at a speed of 8000 r / min, and then 24.0 g of bentonite and 0.84 g of anhydrous sodium carbonate were added, and high-speed stirring was continued for 20 min, and the stirring was stopped at least twice to scrape the bentonite adhered to the wall of the high-speed stirring cup, and then 0.5 g of polyacrylamide with a molecular weight of 5 million and a hydrolysis degree of 25-30% and a solid content of ≥90% was slowly added, and high-speed stirring was continued for 20 min, and the stirring was stopped at least twice to scrape the bentonite and polyacrylamide on the wall, and the fresh water base slurry was obtained after being sealed and cured at 25±2℃ for 24 h.

[0053] The prepared fresh water base slurry was high-speed stirred at 8000 r / min for 5 min, and the 100 r / min reading was tested according to the standard GB / T16783.1-2014, and the value was required to be between 100-120, and if it did not meet the requirements, bentonite was added to meet the index requirements.

[0054] (2) Fresh water base slurry viscosity reduction rate and apparent viscosity reduction rate refer to the standard "SY / T5695-2017 Two-sex ion polymer for drilling fluid viscosity reducer": the specific detection method is as follows: High temperature viscosity reduction rate determination: three 400 mL portions of the prepared fresh water base slurry were taken and placed in high temperature aging tanks, and were placed in a roller heating furnace set at a temperature of 200℃, 220℃ and 240℃, and were heated and rolled for 16 h, and after cooling to room temperature (25℃), high-speed stirring was carried out at 8000 r / min for 5 min, and the 100 r / min reading was determined according to the standard GB / T16783.1-2014, and was recorded as R 100 ; three 400 mL portions of the prepared fresh water base slurry were taken, and 0.4 g of sulfonated lignin prepared in the examples or comparative examples was added as a viscosity reducer at a stirring speed of 8000 r / min, and high-speed stirring was carried out at 8000 r / min for 20 min, and was placed in a high temperature aging tank, and was placed in a roller heating furnace set at a temperature of 200℃, 220℃ and 240℃, and was heated and rolled for 16 h, and after cooling to room temperature, high-speed stirring was carried out at 8000 r / min for 5 min, and the 100 r / min reading was determined according to the standard GB / T16783.1-2014, and was recorded as R 100（1） . The viscosity reduction rate was calculated according to formula (2): D=[R 100-R 100(1) ] / R 100 ×100% (2) Formula (2): D: viscosity reduction rate, %; R 100 : reading at 100 r / min of fresh water base mud, mPa-s; R 100(1) : reading at 100 r / min of fresh water base mud after adding viscosity reducer, mPa-s.

[0055] The test results are shown in Table 2.

[0056] (3) Test of shear stable viscosity: Take the prepared fresh water base mud, add the sulfonated lignin prepared in the examples or comparative examples as a viscosity reducer to obtain a test slurry, and the concentration of the viscosity reducer in the test slurry is 3wt%. The test slurry is placed on a high-speed mixer and sheared at a speed of 12000 rpm for 30 minutes. After high-speed shearing for 30 minutes, the stirring is immediately stopped, and the slurry is poured into the sample cup of a rotary viscometer. The reading at 600 rpm after shearing is measured and recorded, denoted as Φ600, and the shear stable viscosity (AV) is calculated according to formula (3). The test results are shown in Table 2.

[0057] AV=Φ600 / 2 (3) (3) The salt tolerance is tested according to the "Water-based drilling fluid for petroleum and natural gas industry" GB / T 16783.1-2014, and the specific detection method is as follows: (4) Test of salt tolerance: Take 400 mL of the prepared fresh water base mud, add the sulfonated lignin prepared in the examples or comparative examples as a viscosity reducer to obtain a test slurry, and the concentration of the viscosity reducer in the test slurry is 3wt%. The test slurry is placed in a roller heating furnace set at a temperature of 220℃ and hot-rolled for 16h to test the apparent viscosity before adding salt. Take 400 mL of fresh water base mud, add the sulfonated lignin prepared in the examples or comparative examples as a viscosity reducer to obtain a test slurry, and the concentration of the viscosity reducer in the test slurry is 3wt%. Then, 60g of sodium chloride (NaCl) is added to simulate formation salt pollution, and the drilling fluid is fully stirred at a stirring speed of 8000r / min to make the salt completely dissolved and uniformly distributed. After the NaCl is completely dissolved, it is loaded into a high-temperature aging tank and placed in a roller heating furnace set at a temperature of 220℃ and hot-rolled for 16h to test the apparent viscosity after adding salt. The salt tolerance is calculated according to formula (4), and the test results are shown in Table 2.

[0058] Salt tolerance = apparent viscosity before adding salt / apparent viscosity after adding salt × 100% (4).

[0059] Table 2: Viscosity reduction rate, shear stable viscosity and salt tolerance results

[0060] As can be seen from the above data, the lignin sulfonate prepared based on the method of the application has good dispersibility, can effectively disperse solid particles (such as clay and other mineral particles) in the water-based drilling fluid, prevent aggregation and precipitation, and reduce the viscosity of the liquid. The lignin sulfonate weakens the hydrogen bond and polar force between the clay particles through adsorption, and destroys the spatial network structure of the clay particles. In addition, the electronegativity of the sulfonic acid group enhances the negative charge on the surface of the clay particles, further enhances the electrostatic repulsion between the particles, prevents the aggregation between the clay particles, and thus plays a role in reducing the viscosity. This is the mechanism of action of lignin sulfonate in reducing viscosity. The application uses a eutectic solvent (choline chloride / 4-hydroxybenzenesulfonic acid / epichlorohydrin) as a solvent and a sulfonating agent at the same time, and combines with microwave enhanced reaction to realize the integration of lignin extraction and sulfonic acid modification, and solves the problems of high pollution, high energy consumption, complicated steps and the like existing in the traditional lignin sulfonation process.

Claims

1. A method for integrated preparation of lignin extraction-sulfonic acid modification based on deep eutectic solvent coupling with microwave, characterized in that, The method comprises the following steps: (1) mixing choline chloride, epichlorohydrin and 4-hydroxybenzenesulfonic acid, and stirring and heating to form a homogeneous transparent liquid to obtain a ternary eutectic solvent system; the molar ratio of choline chloride, epichlorohydrin and 4-hydroxybenzenesulfonic acid is 1: (1-4): (5-20); (2) adding biomass powder into the ternary eutectic solvent system obtained in step (1) and performing reaction under microwave condition; after the reaction is completed, the obtained filtrate is filtered, and the pH of the filtrate is adjusted to neutral to obtain a mixed solution; then, ethanol is added to the mixed solution to precipitate, and the precipitate is filtered, washed and dried to complete lignin extraction and sulfonic acid modification, thereby obtaining the sulfonated lignin for the environmentally-friendly water-based drilling fluid; the biomass powder is wheat straw powder, corn straw powder or birch stem powder; the mass ratio of the biomass powder to the ternary eutectic solvent system is 1:8-15; and the power of the microwave is 800-1300 W.

2. The method according to claim 1, wherein the method is characterized by, In step (1), the molar ratio of choline chloride, epichlorohydrin and 4-hydroxybenzenesulfonic acid is 1:2:

10.

3. The method according to claim 1, wherein the method is characterized by, In step (1), the temperature of the stirring and heating is 40-70 °C.

4. The method according to claim 1, wherein the method is characterized by, In step (2), the particle size of the biomass powder is 500-1000 nm.

5. The method according to claim 1, wherein the method is characterized by, In step (2), the mass ratio of the biomass powder to the ternary eutectic solvent system is 1:

10.

6. The method according to claim 1, wherein the method is characterized by, In step (2), the power of the microwave is 1000 W.

7. The method according to claim 1, wherein the method is characterized by, In step (2), the temperature of the reaction is 60-100 °C; and the reaction time is 1-8 h. 8.The method of claim 1, wherein the method is characterized by, In step (2), the pH is adjusted to neutral by using a hydrochloric acid solution with a concentration of 1 wt%; The volume ratio of the ethanol to the mixed solution is 1-4:1; the precipitation time is 20-40 min; the washing is performed by using anhydrous ethanol; and the drying is performed at 60-70 °C under vacuum for 15-20 h.

9. An environmentally friendly sulfonated lignin for use in water-based drilling fluids, characterized in that, The sulfonated lignin for the environmentally-friendly water-based drilling fluid is obtained by using the preparation method in any one of claims 1-8.

10. The use of the sulfonated lignin according to claim 9, as a viscosity reducer in the environmentally friendly water-based drilling fluid, characterized in that, The addition amount of the sulfonated lignin for the environmentally-friendly water-based drilling fluid in the environmentally-friendly water-based drilling fluid is 3-6 wt%.

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